KR20100132465A - Use of structured packings which have one or more backup layers and one or more separation layers - Google Patents

Abstract

PURPOSE: A usage of a structured packing including more than one back-up layer and a separation layer is provided to reduce the height of a column for the extractive distillation for a separating function. CONSTITUTION: A usage of a structured packing including more than one back-up layer and a separation layer is for secure the separating efficiency for performing the extractive distillation method of distillate-extracting a material from a mixture. The structured packing includes a back-up layer(1) and a separation layer(2).

Description

Use of structured packings which have one or more backup layers and one or more separation layers}

The present invention relates to the use of structured packings having at least one backup layer and at least one separating layer.

EP-A 1 074 296 discloses, by suitable adjustment of the liquid and gas amounts, that a foam layer, mainly with a dispersed gas phase, forms in a targeted manner the first region, in particular the lower region, of the packing layer and at the same time mainly has a continuous gas phase. Heat exchange between the liquid and the gas in the column, in which the film flow of the liquid has at least one packing layer having a variety of internal structures depending on the height in such a way that it forms a second region, in particular an upper region, of the packing layer and Structured packing for mass transfer is disclosed.

This packing is in the form of a transition between a packing column with a predominantly dispersed liquid phase and a tray column with a predominantly continuous liquid phase, and advantageous properties of the packing column, in particular drop entrainment and further prevention of mass transfer on the packing surface. Together they combine the advantageous properties of the tray column, in particular the high mass transfer performance in the foam layer.

In particular for columns with such packing, the separation efficiency is substantially up to 60% higher compared to columns with conventional structured packing. The separation efficiency of a column is typically defined as the theoretical number of columns per meter of column height (n _th / m) or the equivalent height of the theoretical stage (hetp).

Extractive distillation is often carried out with the addition of a selective solvent for the distillation separation of a mixture of substances whose liquids comprise very similar components. The solvent of choice is a substance or mixture of substances having a higher boiling point than the substance to be removed. The optional solvent as an additive of the material mixture to be separated by extractive distillation is only about 15 to 60, whereas the efficiency of the plate in the extractive distillation is about 70 to 80% for classical distillation without addition of the selective solvent. It has a result of%.

Thus, in order to separate the material by extractive distillation, a high height packing and a corresponding column are required.

Therefore, it is an object of the present invention to improve the separation efficiency of the column for extractive distillation or to reduce the column height of the extractive distillation for the same separation function.

SUMMARY OF THE INVENTION

Structured packing with one or more backup layers having a specific surface area selected to reach or exceed the flooding point in one or more backup layers, and one or more separation layers having a specific surface area selected to not reach the flood point of,

It is achieved by use as an internal having a separation effect in a column for carrying out a method of distilling off a substance from a mixture comprising the substance by extractive distillation with the addition of a selective solvent.

1 shows a packing layer of one embodiment of structured packing for use according to the invention.
2 shows the packing member aligned back and forth of the packing layer of a further embodiment of the structured packing for use according to the invention.
3 shows the packing member aligned back and forth of the packing layer of a further embodiment of the structured packing for use according to the invention.

Since the cleaning after soiling is difficult, and the structured packing is always customizable, so procurement of replacements is time consuming and expensive, the use of structured packing in the extractive distillation process with the addition of high-boiling solvents is important. It is known to process technicians for.

In particular, in the case of distillation separation of C ₄ fractions, i.e. mixtures of hydrocarbons comprising predominantly hydrocarbons with four carbon atoms per molecule, contamination due to the tendency of polymerization of components with conjugated double or triple bonds, The risk increases. In addition, many of the selective solvents classified for extractive distillation tend to cause contamination.

In contrast, surprisingly, the present inventors have found that certain structured packings have one or more backing layers that reach or exceed the flood point and one or more separation layers that do not reach the flood point and that have a specific structured packing that varies in height depending on height. By using according to the present invention, it has been found that sufficiently high turbulence can be ensured in the backup layer or the backup layers, thereby controlling the risk of contamination in the extractive distillation, especially the extractive distillation of the C ₄ fraction. This can be explained from the significant turbulence cleaning effects of the gas and liquid phases.

According to the invention, the structured packing as described in EP-A 1 074 296, ie by means of suitable adjustment of the liquid and gas amounts, the foam layer mainly with the dispersion gas phase is subjected to the first region of the packing layer, in particular It has a variety of internal structures depending on the height, in such a way that the film flow of the liquid, which at the same time forms the lower region, and at the same time mainly forms the second region of the packing layer, in particular the upper region, in a targeted manner, the first lower end and Packing with one or more packing layers having a second upper end is used.

The structured packings are arranged perpendicular to each other in a regular structure and are very generally in assembly, assembled together by means of fastening means, for example metal wires, thin metal rods or sheet metal strips, expanded metal sheets. metal) and a plurality of individual layers of packing members such as wire fabrics. Generally, such a packing member has a geometry, for example in the form of a bend or a circular hole having a diameter of about 4 to 6 mm. The opening serves to increase the overflow limit of the packing and to allow higher column loads.

The described hydraulic operating state can be achieved by varying the flow resistance with respect to the height of the packing layer. Preferably, the first region, optionally the lower region, of the packing layer has a higher flow resistance than the second region, optionally the upper region, of the packing layer.

The first region of the packing layer is preferably present in the lower region of the packing layer and the second region of the packing layer is preferably present in the upper region of the packing layer. For the purposes of the present invention, the first region, optionally the lower region and the second region, optionally the upper region, of the packing layer preferably extends over the total cross-sectional area of the packing layer. The first lower region of the packing layer will immediately adjoin the lower end of the packing layer and the second upper region of the packing layer will immediately adjoin the upper end of the packing layer. In a preferred embodiment, the first region, optionally the lower region, of the packing layer is immediately adjacent to the second region, optionally the upper region.

Structured packings are advantageously sheet-metal or fabric packings formed from flat metal sheets or fabric layers having a cross-channel structure.

In particular, the flat metal sheet or fabric layer forming the cross-channel structure has a bend at an angle of less than 60 °, preferably 45 ° with respect to the horizontal plane in one or more separation layers.

The sheet-metal or fabric packing is preferably formed in a cross-channel structure so that in each case two to ten, preferably two to four bends of intersection points are above the height of the separating layer.

The height of the at least one separating layer is in each case 5 to 50 cm, preferably in each case 10 to 20 cm.

For the use according to the invention, one or more substances are used as the selection solvent which leads to an increase in the relative volatility of the substance to be separated (ie the desired product) compared to the other components of the mixture containing it. In general, this is a high-boiling substance, ie a substance having a higher boiling point compared to the mixture to be separated. Particularly preferably, high-boiling polar substances selected from N-methylpyrrolidone, dimethylformamide and acetonitrile, or mixtures thereof are used as the selection solvent.

Preferably, one or more additives, in particular water and / or one or more C ₁ -C ₄ -alcohols, can be added to the selection solvent. Monohydroxy alcohols or diols can be used as C ₁ -to C ₄ -alcohols. Preference is given to methanol and n-propanol or isopropanol.

Preferably, extractive distillation may be carried out in the presence of at least one stabilizer having a boiling point higher than that of the material to be separated in order to further limit the tendency of polymerization.

The invention also relates to the use of structured packings having at least one backup layer and at least one separation layer in a process for separating a mixture which is a C ₄ fraction by extractive distillation to be separated.

Preference is given to the use in the process of separating 1,3-butadiene from the C ₄ fraction by extractive distillation and / or separating butane and butene from the C ₄ fraction.

The present invention is not limited to any particular procedure for separating 1,3-butadiene from C ₄ fractions.

According to the invention, the structured packing is preferably as described in DE 101 05 660, ie a split wall column and a split wall column upstream with a split wall where the separation of the C ₄ fraction leads up to the upper end of the split wall column. In the process carried out in the washing column, it can be used in a column to obtain 1,3-butadiene by extractive distillation.

More preferably, structured packings having various internal structures depending on the height are used in the process for separating 1,3-butadiene from C ₄ fractions as described in DE 103 22 655.

Thus, the partition wall is extracted with the formation of the first partial region, the second partial region and the lower common column region, the partition wall column being longitudinally aligned with the column and leading up to the upper end of the column and connected to the upstream extraction wash column. Used for distillation.

Preferably,

The C ₄ fraction is fed to the first partial region, preferably their middle region, of the dividing wall column,

Supplying a top stream from the first partial region of the split wall column to the bottom region of the extraction wash column,

Countercurrent extraction by treatment of the selected solvent with the first partial-stream in the upper region of the extraction wash column is carried out in the extraction wash column,

The component of the C ₄ fraction which is less soluble than 1,3-butadiene in the optional solvent is removed through the top of the extraction wash column,

Recycle the bottoms stream from the extraction wash column to the top region of the first partial region of the partition wall column,

Supplying a second partial-stream of the selective solvent to the upper region of the second partial region of the split wall column,

Remove the top product from the second partial region (B) of the split wall column as crude 1,3-butadiene,

The bottoms stream of purified solvent recycled to the process is removed from the bottom common column of the split wall column.

Thus, preferably, the C ₄ fraction to be separated is supplied to the first partial region, particularly preferably their middle region, of the split wall column and the top stream from the first partial region of the split wall column is subjected to an upstream extraction wash column. Reflux extraction by feeding to the bottom region of the extract, treatment of the selected solvent in the upper region of the extract wash column with a first sub-stream, is carried out in the extract wash column and is less soluble than 1,3-butadiene in the selected solvent. The components of the C ₄ fraction are removed through the top of the extraction wash column, particularly preferably condensed in the condenser at the top of the extraction wash column and partly added back to the extraction wash column as reflux, otherwise frequently raffinate 1 Butane and butene, referred to as, are mainly removed as by-products.

The bottoms stream of the extract wash column, i.e. a stream comprising components of 1,3-butadiene, butane, butene, and C ₄ fractions more soluble than 1,3-butadiene in the selected solvent, in addition to the selected solvent, By supplying to the upper region of the partial region, a countercurrent extraction with removal of less soluble components than 1,3-butadiene in the selected solvent, is added to the C ₄ fraction in the form of steam in the upper region of the first partial region of the split wall column. Mass transfer between the stream and the stream can be carried out at the top of the first partial region of the partition wall column.

At the lower end of the dividing wall, a vapor stream is obtained which comprises, in addition to 1,3-butadiene, a component of the C ₄ fraction which is more soluble than 1,3-butadiene in the selected solvent, in particular C ₄ -acetylene. They are washed from a rising vapor stream which is a countercurrent flow with a second sub-stream of the selective solvent added to the upper region of the second partial region of the split wall column. Remove the vapor top product from the second partial region of the partition wall column, preferably condense it in the condenser at the top of the column, and reflux the partial-stream of the condensed top stream to the partial region (B) of the partition wall column. And the condensed top stream as crude 1,3-butadiene.

In the bottom common column region, complete degassing of the solvent is carried out and the purified solvent is obtained at the bottom of the extractive distillation column.

In determining the energy input required for this, via the bottom evaporator of the extractive distillation column, the process engineer will consider the mixture of materials or the heat loading capacity of the materials used in each case in certain cases as the optional solvent.

In a further preferred embodiment, the extractive distillation for separating 1,3-butadiene from a C ₄ fraction is likewise carried out in a plant comprising a split wall column having a split wall connected to an upstream extraction wash column and extending to the top end of the column. However, in contrast to the embodiment described above, the C ₄ fraction to be separated is supplied to the lower region of the upstream extraction wash column rather than to the first partial region of the split wall column.

It is not absolutely necessary to provide a recovery of the by-product, including butane and butene, the so-called raffinate 1, in an upstream extraction wash column separated from the extractive distillation column. In view of the specific boundary conditions for the process, in particular the composition of the C ₄ fraction to be separated and the specification of Raffinate 1, it is technically and economically feasible to increase the theoretical number in the first partial region of the split wall column. In the case, it is also possible to integrate the extract wash column into the first partial region of the split wall column used as the extract distillation column.

The use according to the invention of structured packings with a backing layer is preferably a process for separating C ₄ fractions by extractive distillation with a selected solvent, in which 1,3-butadiene, butene and butane are in each case obtained as separate streams. Can be used for

The present invention is not limited to any particular procedure for separating C ₄ fractions into 1,3-butadiene, butane and butenes.

The extractive distillation is carried out in accordance with WO 2004/011406, which is carried out in a column which is aligned in their longitudinal direction and which leads to the upper end of the column and thus forms a first upper region, a second upper region and a lower common column region. Use in the process is preferred, wherein the top stream comprising butane is separated from the first upper region and the top stream comprising butene is separated from the second upper partial region and is more soluble than butane and butene in the optional solvent A stream comprising hydrocarbons from the phosphorus C ₄ fraction is separated from the bottom common column zone.

Preferably, a stream may be fed to the first distillation column which is removed from a split wall column having a split wall extending completely to the top end of the column and comprises hydrocarbons which are more soluble than butane and butene in the selected solvent, wherein the stream is 1,3-butadiene, propene, optionally further low boiler, optionally a top stream comprising water, and 1,3-butadiene, 1,2-butadiene, acetylene and optionally further high boiling material And the ratio of butadiene in the bottoms stream of the first distillation column is at least high enough to dilute the acetylenes outside the range of risk of spontaneous decomposition, and the top stream of the first distillation column is Top stream and pure water 1 which are fed to a second distillation column and comprise propyne, optionally further low boilers, optionally water It is adjusted in a manner that separates into a bottoms stream comprising 3-butadiene.

The invention also relates to the use of structured packings having at least one backup layer and at least one separation layer in a process wherein the mixture is separated by extractive distillation and the material to be separated by extractive distillation is isoprene.

The invention will be explained in more detail below with reference to the drawings.

1 shows an embodiment of structured packing for use according to the invention. Packing layer 1 has a first lower end and a second upper end. The height H is 0.2 m, for example. The packing has a touching flat packing member 4 comprising a flat metal sheet 3 with bends (not shown). Reference numeral 4 designates the longitudinal axis of the packing. The packing has a circular cross section. The internal geometry of the packing varies with their height (not shown). The packing has a first bottom backup layer 1 whose internal geometry is different from the second top separation layer 2. The backup layer 1 has a higher flow resistance than the separation layer 2. By suitably adjusting the amounts of liquid and gas, an effervescent layer mainly with a dispersed gas phase is formed in the backup layer 1 and a film flow of liquid mainly with a continuous gas phase is formed in the separation layer 2. The backup layer 1 and the separation layer 2 extend over the total cross sectional area of the packing.

2 and 3 show different embodiments of structured packings for use according to the invention, in each case schematically showing a flat metal sheet 3 aligned back and forth. The solid line represents the path of the bent portion of the flat metal sheet 3, such as the first, third, and fifth, and the dotted line represents the path of the bent portion of the flat metal sheet 3, such as the second, fourth, and sixth.

1 .: backing layer
2 .: Separation layer
3 .: flat metal sheet
4 .: longitudinal axis of packing

Claims (15)

As internals having a separation effect in a column for carrying out a method of distilling off the material from a mixture comprising the desired material by extractive distillation to which a selected solvent is added,
At least one backup layer (1) having a specific surface area selected to reach or exceed a flooding point in at least one backup layer (1), and at least one separation layer having a specific surface area selected to not reach the flood point Use of structured packing comprising (2). The method according to claim 1, wherein the specific surface area of the at least one backup layer (1) is selected such that the flood point in the at least one backup layer (1) is from 10% to 100%, preferably from 20% to 50%, and at least one separation layer The specific surface area of (2) is selected so that the flood point in one or more separation layers (2) is 20% to 80%, preferably 30% to 50%. The use according to claim 1 or 2, wherein the structured packing is a sheet metal or fabric packing formed from a flat metal sheet (3) or fabric layer having a cross-channel structure. 4. The flat metal sheet or fabric layer forming the cross-channel structure comprises bends at an angle of less than 60 degrees, preferably 45 degrees, with respect to the horizontal plane of the at least one separating layer (1). Usage. 4. The cross-channel structure according to claim 3, wherein the sheet metal or fabric packing is such that the intersections of the bends present above the height of the separating layer (1) are in each case 2 to 10, preferably 2 to 4, in each case. Uses formed. Use according to claim 1 or 2, wherein the height of the at least one separating layer is in each case 5 cm to 50 cm, preferably in each case 10 cm to 20 cm. The use according to claim 1 or 2, wherein the extractive distillation is carried out in the presence of at least one stabilizer having a boiling point higher than that of the material to be separated. The solvent according to claim 1 or 2, wherein, as the selection solvent, the boiling point is higher than that of the material to be separated, and is preferably selected from N-methylpyrrolidone, dimethylformamide and acetonitrile, or a mixture thereof. The use of one or more polar substances with or without addition of them. The use according to claim 8, wherein an additive is added to the selected solvent. The use according to claim 9, wherein the additive added is water and / or C ₁ -C ₄ -alcohol. Use according to claim 10, wherein the C ₁ -C ₄ -alcohol used is ethanol, n-propanol or isopropanol. The use according to claim 1 or 2, wherein the mixture to be separated by extractive distillation is a C ₄ fraction. 13. Use according to claim 12, wherein the substance to be separated by extractive distillation is 1,3-butadiene. 13. Use according to claim 12, wherein the fraction comprising mainly butane and the fraction comprising mainly butene are separated by extractive distillation. The use according to claim 1 or 2, wherein the substance to be separated by extractive distillation is isoprene.

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